A major goal of HIV-1 research is the development of agents that target non-enzymatic stages of the viral replicative cycle. HIV-1 entry involves a cascade of events that are vulnerable to therapeutic intervention, including gp120-CD4 attachment, gp120-co-receptor interactions, and gp41-mediated fusion. Clinical trials of agents such as T-20 have validated HIV-1 entry as a therapeutic target, but there is an urgent need for orally available agents suitable for chronic administration. The goal of this Phase I project is to identify small-molecule inhibitors of HIV-1 entry. A novel, virus-free fluorescence Resonance Energy Transfer assay that accurately reproduces all stages of HIV-1 entry will be used for high throughput screening of combinatorial chemical libraries. Active compounds will be analyzed for specificity, potency, and breadth of antiviral activity and further characterized as attachment, co-receptor or fusion inhibitors. During the Phase II project, active compounds will be optimized for antiviral properties, tolerability and oral availability using traditional, combinatorial, and computational chemistry. The optimized agents will be examined for potency, breadth, and durability of antiviral effects using the best available models of HIV-1 infection. This project combines advanced screening methods, the emerging field of combinatorial chemistry, and state-of-the-art virologic models for the development of new, orally available inhibitors of HIV-1 entry. PROPOSED COMMERCIAL APPLICATIONS: This project seeks to develop a novel class of anti-HIV-1 agents. For an orally available drug that safely and effectively blocks an early step of the HIV-1 replicative cycle and for which there are no comparable therapies, the market would be HIV-infected individuals who are suboptimally treated by existing therapies. These individuals include those with measurable viral loads despite highly active antiretroviral therapy and those who experience significant treatment toxicities. Currently, these individuals comprise a sizeable if not majority fraction of HIV-infected individuals, who currently number approximately 900,000 in the U.S.